Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

With no annotations, the description must carry the behavioral load, and it discloses a genuinely non-obvious trait: the call costs $0.005 USDC on Base via x402. It also makes the response content predictable. It stops short of covering failure modes or latency, but the paid-call disclosure is the piece an agent most needs before invoking.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Is the description appropriately sized, front-loaded, and free of redundancy?

Two sentences, front-loaded with the purpose and returned fields, with the pricing note second. No filler, no repetition of the tool name, and nothing that could be cut without losing information.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

No output schema exists, so the description appropriately enumerates the four returned values, and all three required params are covered by the schema. What's missing is minor: the actual response shape/field names and behavior on invalid or unapproved pairs.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema description coverage is 100% and all three parameters are documented (owner grants, token is the ERC-20 contract, spender is allowed to spend). The description's 'a spender may transfer from an owner' restates those roles in allowance terms but adds no format or constraint detail beyond the schema, so the baseline 3 applies.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Does the description clearly state what the tool does and how it differs from similar tools?

Names the exact resource (ERC-20 allowance), the chain (Polygon PoS), and enumerates what is returned: allowance amount, unlimited-approval flag, owner balance, and current spendable amount. The chain qualifier cleanly separates it from eth_erc20_allowance, base_erc20_allowance and the other chain-prefixed siblings without needing the schema.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Does the description explain when to use this tool, when not to, or what alternatives exist?

Usage is only implied: phrases like 'whether the approval is effectively unlimited' hint at a token-approval security review, but there is no explicit when-to-use, no exclusion, and no pointer to alternatives such as polygon_wallet_balances or polygon_token_snapshot. An agent must infer whether to call this or a broader balance/snapshot tool.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.